Concrete building construction



Oct. 13, 1964 K. H. MIDDENDORF CONCRETE BUILDING CONSTRUCTION 12Sheets-Sheet 1 Filed Nov. 17. 41958 INVENTOR. KARL H. M/DE/VAF ATTORNEYOct. 13, 1964 K. H. MIDDENDORF 3,152,421

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Oct. 13, 1964 Filed Nov. 17, 1958 K. H. MIDDEN DORF CONCRETE BUILDINGCONSTRUCTION l2 Sheets-Sheet 6 KARL BY WEE@ Oct. 13, 1964 K. H.MIDDENDORF 3,152,421

CONCRETEBUILDING CONSTRUCTION Filed Nov. 17, 1958 12 Sheets-Sheet '7 affig. I0

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Oct. 13, 1964 K. H. MIDDENDORF 3,152,421

CONCRETE BUILDING CONSTRUCTION Filed Nov. 17. 1958 12 Sheets-Sheet*l 9INVENTOR. 73 68 KARL ht M/DDENDQRF Fig.13 BY A from/,5y

K. H. MIDDENDORF CONCRETE BUILDING CONSTRUCTION Oct. 13, 1964 12Sheets-Sheet 11 Filed Nov. 17, 1958 F Y .e E R0 ma Fm NN 0 EE .r W@ frIm 9M IH. .WM FKW 8 6 9 n n M United States Patent O 3,152,421 CNCRETEBUILDING CGNSTRUCTIN Karl H. Middendorf, Costa Mesa, Calif., assigner toThe Prescon Corporation, a corporation of Texas Filed Nov. 17, 1958,Ser. No. 774,293 6 Claims. (Ci. 'S0-128) My invention relates toconcrete-building construction, and more particularly to a concretebuilding construction that includes a floor or roof slab having portionsof a grid-like character, comprising spaced longitudinally andtransversely extending intersecting frame members deining openingsbetween the same, between supporting means, such as columns.

In a building construction having a roof or floor slab of the abovereferred to character, there are areas of solid concrete at and adjacentthev columns, that are mounted on the columns, and form cap portions forthe columns, It is one of the important purposes` of my invention toprovide a construction for prestressing said solid concrete areas so asto create high horizontal pressures by menas of which the shear existingin these areas can be fully met. In order to accomplish this purpose, itis desirable that the prestressing tension members can be placedanywhere desired in the depth of the slab of solid concrete around thecolumn and to mount thel tension members in the concrete in such amanner that these normally will be as nearly straight as possible.

It is a particular purpose of my invention to provide open toppedpockets or chambers in the slab at the mar.- gins of the solid area inorder that the tension members can be provided at any desired depth inthe concrete and can normally be placed in the concreterin as nearly astraight line as possible and can be readily tensioned economically andwithout difculty with well known apparatus that is at present in use andwithout the use of expensive anchoring means for the tension members,and Without putting sharp bends in the tension members.

In order to provide for the prestressing of the solid area of concreteadjacent the columns, I provide said open topped pockets along themargins of the solid concrete area and have these arranged opposite-eachother so that the tension members can be extended from one of saidpockets to the opposite pocket and provide a construction in whichpockets can be made of such a size that no diiculty is encountered inproviding the tension members at any depth that they may be desired and`at any location in the solid concrete that it may be desired and so thatthere is no lack of space for equipment necessary for stressing thetension members.

It is a further purpose of my invention to provide a method of formingthe above referred to open topped pockets in the slab such that theform'rnembers for said open topped pockets can be removed as soon as theinitial set of the concrete has taken place, usually two or three hoursafter pouring, and so that the form members that provide the voids orspaces between the intersecting members of the grid-like structure canbe similarly removed. In order to accomplish this purpose, said formsare of such a character that the same can be disassembled or collapsedand removed upwardly through the tops of the openings provided in theconcrete structure by means of said forms without disturbing thesupporting means under the forms and under the setting concrete.

My improved concrete construction and method of manufacturing the slabcan be used both in connection with a slab that is cast in-situ or inlift-slab construction.

Considerable advantage exists in the fact that the forms can be removedlong before the concrete has set to its maximum strength, because thisenables the re-use of the forms in other portions of the structure or inother 3,152,421 Patented Oct. 13, 1964 ICC similar structures longbefore it would be possible to do this if the forms were not removablein an upward direction, as, otherwise, it would be necessary to waituntil the concrete had reached suicient strength that the supportingmeans, such as shoring under the slab, could be removed with safety.

The grid-like structure could be described as being a ribbed structurewith ribs on all four sides of each of the quadrangular openingstherein. In my improved construction it is possible to provide anydesired spacing 0f the ribs from each other, or in other words, any sizeof the opening that may be desired, and the openings may be of anyquadrangular character, that is, square, rectangular or trapezoidal.

When my improved slab construction is used as a lift slab construction,a further advantage exists in that the area of solid concrete that is tobe around the columns can be prestressed before the slab is raised intoposition for mounting on the column.

It is a further purpose of my invention in lift slab construction toprovide a means for supporting the slab on the columns that eliminatesthe use of expensive shear or lifting collars and in which all parts ofthe apparatus mounted in the slab for lifting purposes can be removedfor further use. This is accomplished by providing columns that havereduced sections at the ultimate location of the slab providingshoulders thereon, which columns extend through openings in the slab,the slab being cast around. said columns, and after reaching itsrequired strength and being prestressed in the manner above referred to,raised to its final position in the structure in such a location thatthe shoulder on the column is located closely adjacent the walls of theopening in the slab, and providing projecting means, such as horizontalribs, in the walls of the opening and filling the space between the`reduced portion ofthe column, the shoulder and the wall of the openingwith quick setting high strength concrete to key the slab to the column.The openings in the slab are made of such' a size that the slab willreadily pass upwardly along the columns as it is lifted, butsufficiently small that there will not be any large gap between the topsurface of the shoulder on the column and the wall of the opening in theslab adjacent thereto.

In carrying out my invention in concrete construction, it is animportant purpose'to provide'a method of making pockets in a concretestructure comprising mounting removable pocket forming means in positionin a form, pouring concrete in the form toy any predetermined levelbelow the top of the pocket forming means but leaving the top exposed,and after the concrete has set sutiiciently to permit removal of thepocket forming means without damage thereto, removing said pocketforming means upwardly through the open top of the pocket, and to carryout this method without removing the supporting means for the forms fromunder the concrete structure.

In carrying out my invention in concrete construction, it is a furtherpurpose to provide means on the removable pocket forms for providinggrooves or recesses in the grid-like structure in which supporting meanscan be placed for the subsequent casting of a continuous slab over thegrid-like structure without providing any sup ports on any rigid areabeneath the grid-like structure.

In carrying out my method, I have provided a new and improved concreteform for forming pockets and similar spaces or voids in a concretestructure, and it is a purpose of my invention to provide such a formwith upstanding corner members and wall forming members extendingbetween them to form a quadrangular enclosure, and provide means forpreventing both outward and inward movement relative to each of theopposing walls of said quadrangular enclosure, comprising detachableholding means engaging the wall forming members to hold the same againstinward movement, that are so constructed and arranged that theconnecting wall forming members are detachable from the corner membersupon disengagement of the holding means from the wall forming members,so that the form can be removed upwardly.

It is an important purpose of my invention to provide a form member thatis removable in an upward direction, which may be collapsed ordisassembled in order to be removed in such an upward direction andwhich is provided with means to prevent either outward or inwardcollapse of the form and to provide a support for a working platformover the opening in the form. It is a further important purpose of myinvention to provide means for supporting the bottom of such a form insuch a manner that it can be removed in an upward direction and toprovide means on the form that provides impressions in the frame membersof the grid structure for supporting suitable means on which a slab maybe cast without providing any supporting shores or similar bracing meansunder the same.

It is a further purpose of my invention to provide such a form memberthat is made up of flat wall forming members that can be readily stackedand which do not have any projecting hardware of any kind thereon andwhich are used in connection with corner posts that are provided withmeans for clamping bar-like holding members thereto that extend from oneof said corner posts to the next corner post along the inner face ofeach of said wall panel members adjacent the top and bottom thereof soas to prevent inward movement of said wall forming members relative toeach other and to thoroughly brace the form. Preferably the bars aremade of ordinary pipe and only the corner posts have to be of anyspecial design.

It is a further purpose of my invention to provide simple means formounting a top wall panel or working deck and a bottom wall panel whendesired on such form so that these can be readily removed to enable theform to be removed from the concrete structure, all parts of the formbeing removable upwardly through the openings created in the concretestructure by the forms.

In my improved slab construction deck slabs that can be made of eitherregular concrete or insulating concrete are adapted to be laid on top ofthe joists or set in pockets, and in floor construction, light weightcovers of light weight concrete, corrugated steel, asbestos, transite oraluminum can be laid over the joists and a slab thick enough to carrythe load and ducts and piping poured monolithically over the entirearea. Furthermore such slabs may be poured on temporary forms carried bysupporting members temporarily fixed in pre-formed impressions in thegrid-like structure. It is to be understood that, depending on thedesign considerations, such superimposed slabs may be free of thesupporting ribs or developed into combined sections of the ribs bybonding the slab with the grid-like structure in a well known manner. Inroof construction, plastic domes can be set in the open spaces betweenthe members of the grid construction forming the quadrangular openingsas sky-lights, should this be desired. As the tops of the pockets areopen, and when covered by a removable slab member, adjustment in thestress created by the tension members can be made at any time aftercompletion of the struc- ,ture should this be found to be desirable.

My improved form member can be made either with wooden side wall panelsheld together in a suitable manner in quadrangular form or of metallicside wall forming sections, an object being to provide a metallic formthat has the advantages of being withdrawable upwardly through anopening created by the form, in a similar Inanner to my form membersutilizing Wooden wall panels. In order to accomplish this purpose aplurality of upstanding wall forming sections are provided that have aipair of wall portions extending perpendicularly to each other and eachof which extend around a corner of the form and members mounted betweenadjacent ends of these wall forming sections, said angular wall formingsections and the members between them being connected together to form aquadrangular enclosure and having bracing means detachably connectedwith the members mounted between said sections and said sections to holdthe opposed wall forming portions of said sections against relativemovement inwardly toward each other or outwardly away from each other.

More specifically it is a purpose of my invention to provide a metallicconcrete form having a plurality of such upstanding wall formingsections that have stiftening formations along the top, bottom and endmargins thereof and members mounted between adjacent ends of these wallforming sections that have a vertical stitfening formation thereon thatis mounted between the end margin stiffening formations of the wallforming sections, and to provide bracing members extending across theend margin stifening members of adjacent sections and detachablyconnected therewith and with the members mounted between the adjacentends of said wall forming sections, and further to provide transversebracing means detachably connected with these members that are mountedbetween the adjacent wall forming sections to hold the opposed wallforming portions of the wall forming sections against relative inwardand outward movement. Furthermore, in the metallic walled form it is afurther purpose to provide top and bottom stiftening formations thatprovide means for mounting a top and a bottom wall member in position onthe form in a similar manner to that used in the form having the woodenside panels, and to provide detachable projecting means on the outerfaces of said wall forming members that provide grooves or recesses inthe grid-like structure for the supporting means for forms for thesubsequent casting of a continuous slab over the grid-like structure.

Other objects and advantages of my invention will appear as thedescription of the drawings proceeds. I desire to have it understood,however, that I do not intend to limit myself to the particular detailsshown or described except as dened by the claims.

In the drawings:

FIG. 1 is a plan View of a portion of a oor or roof slab made inaccordance with my invention.

FIG. 2 is a fragmentary enlarged vertical sectional view taken on theline 2-2 of FIG. 1.

FIG. 3 is a fragmentary section taken on the line 3 3 of FIG. 2.

FIG. 4 is a fragmentary plan view on an enlarged scale of the marginalportion of the slab shown in FIG. 1.

FIG. 5 is a fragmentary plan view on an enlarged scale of a portion ofthe structure shown in FIG. 1, with the forms in position but the toppanels thereof removed.

FIG. 6 is a vertical sectional view taken substantially on the line 6-6of FIG. 5, but showing the top walls of the form members in position.

FIG. 7 is a view partly in section and partly in plan of the portion ofthe structure shown in FIG. 4, but prior to removal of the forms andtensioning of the tension members.

FIG. 8 is a section on an enlarged scale taken on the line 8 8 of FIG. 1after removal of the forms.

FIG. 9 is a fragmentary vertical sectional View through a portion of thegrid structure in a lift slab construction, showing the forms inposition and the slab in its position prior to being lifted.

FIG. 10 is a view similar to FIG, 9 of a grid construction in which theslab is cast in-situ.

FIG. 11 is a fragmentary plan view on an enlarged scale of the cornerportion of the form, showing the corner post and portions of the wallpanels and holding means therefor.

FIG. 12 is a fragmentary vertical sectional View taken on the line 12-12of FIG. 11, but showing the top wall panel in position.

FIG. 13 is a similar view taken on the line 13-13 of FIG. 11.

FIG. 14 is a fragmentary vertical sectional View of a portion of a gridstructure made in accordance with my invention, showing one form ofremovable slab structure mounted thereon.

FIG. 15 is a similar view showing a different mounting for the removableslab structure.

FIG. 16 is a plan View of a. modified form of form with the top thereofremoved.

FIG. 17 is a fragmentary vertical sectional view taken on the line 17-17of FIG. 16.

FIG. 18 is a fragmentary section on an enlarged scale taken on the line18-18 of FIG. 17.

FIG. 19 is a similar view taken on the line 19-19 of FIG. 17.

FIG. 20 is a similar view taken on the line Ztl-2t) of FIG. 17.

FIG. 21 is a fragmentary View partly in section and partly in elevationtaken on the line 21-21 of FIG. 16.

FIG. 22 is a fragmentary section similar to FIG. 20 of a modification.

FIG. 23 is a fragmentary section of a concrete `structure resulting fromthe modified form shown in FIG. 22, and

FIG. 24 is a fragmentary section taken on the line 24-24 of FIG. 17.

Referring in detail to the drawings, in FIG. 1 is shown a portion of alift slab that embodies my invention. Said lift slab is mounted on apost 20, which is shown as being of concrete, the lift slab having asolid area 21, which constitutes a cap portion mounted on the post 20.Extending between each of the posts 20 from the solid area 21 adjacentsaid post and supported thereby and the next post thereto, similarlyprovided with a solid portion 21, is a grid structure, the posts beingarranged in rows both transversely and longitudinally of the slab. Saidgrid structure comprises a plurality of parallel frame members or joists22, which extend in one direction in said structure, and similar framemembers or joists 23 that extend transversely to said first mentionedframe members or joists, said joists or frame members 22 and 23intersecting at right angles to each other as shown in the drawings, thesame being integrally united with each other at said intersections 24.Thus the members 22 extend along one pair of opposite sides and themembers 23 extend along the other pair of opposite sides of the openings25 in said grid-like structure, which extend entirely through the same.The frame members or joists along the marginal edge of the slabpreferably widen so as to provide sufcient cross section thereof at theends of said frame members for accommodating the tension members thatare preferably provided in each thereof. The widened portions of theframe members 22 are indicated at 22' and instead of the openingsbetween the joists 22 being rectangular, as is true of the openings 25,said openings 25 are trapezoidal. Itis, of course, to be understood thatall the marginal ends of both the frame members 22 and 23 are similarlymade.

The frame members 22 and 23 are provided with tensionmembers 26, whichextend longitudinally thereof in any desired arrangement to obtain thedesired prestressed condition of said tension members for their span andthe load that they are to carry. While a plurality of tension membersboth vertically and horizontally of each of said frame members 22 and 23extending from one marginal edge to the other marginal edge of the slabwould ordinarily be provided, in FIG. l, due to the small scale of thedrawing, the tension members in each of the joists or frame members aremerely indicated by a single dotted line in each of said frame membersor joists. Said tension members, as will be obvious from FIG. 1,traverse the solid area 21 around each of the posts 20.

In a structure of the character forming the subject matter of myinvention, whether a lift slab construction is provided or a castin-situ construction is provided, the area of solid concrete 21 aroundeach of the posts is subjected to a great amount of shear, and in orderto provide said solid area 21 with means for resisting this shear, meansis provided for prestressing this area in both directions. Tensionmembers 27, 28, 29 and 30 are provided for this purpose. Said tensionmembers extend between pockets 31 and 32 at the marginal edges of thesolid area 21. It will be noted in the form of slab shown in FIG. 1 thatthere are a plurality of pockets along each marginal edge of the solidarea 21, the pockets 31 having the tension members 27 and 23 extendingbetween the same, the tension members 27 and 28 extending at rightangles to each other, while the pockets 32 only have the tension members29 and 30 extending between the same, the tension members 29 extendingbetween one pair of pockets 32 and the tension members 30 extendingbetween another pair of pockets 32.

The ends of said tension members terminate in said pockets 31 and 32 andin recesses 33 in the marginal portions of the slab. Suitable anchoringmeans for the tension members are provided. The anchoring means may beof any preferred or desired character, but are shown for the tensionmembers 26 in FIG. 4 as comprising an anchor plate 34, a collar 35 andspacing members 36, which are inserted between the collar 35 and theanchor plate 34 after the collar 35 has been moved to the position shownin FIG. 4 by a suitable hydraulic jack engaging with the collar 35 in asuitable manner. Preferably the tension members 26 have heads 37 thereonthat engage the adjacent face of the collar 35 to hold said tensionmembers in assembled position with respect to said collar and instressed condition after insertion of said spacing members 36. Thetension members 27, 28, 29 and 30 are similarly anchored in the pockets31 and 32. While FIG. 1 of the drawings shows some characteristics of alift slab construction that would not be present in a slab cast in-situ,the above referred to structural features would be present in a slabcast irl-situ or a lift slab. While the formations 31 and 32 arereferred to as pockets, the use of this terminology is not intended tohave any bearing on the size of the voids provided in these locations,as said pockets provide rather large chambers in which suicient spaceexists for the placing of the anchoring members for the tension membersand the tensioning of said tension members.

The pockets 31 and 32 and the openings 25 are provided by means of formsthat are substantially the same in construction, the forms being of sucha character that the parts thereof are removable upwardly through theopen tops of t'ne openings 25 and the open tops of the pockets 31 and32. The forms are of such a character that any quadrangular opening orpocket can be provided by means of the same, by slight variations in thepositioning of the walls thereof, and said pockets or openings may besquare, rectangular or of any other suitable quadrangular shape. While acertain arrangement of pockets around the column is shown in FIG. 1, thearrangement of pockets and of tension members extending between thepockets will vary in accordance with the load that will be sustained bythe solid concrete area 21, which is dependent upon the number of joistsor frame members 22 and 23 that are positioned between each of saidsolid areas 21 and the next adjacent solid area 21 in either directionin the slab. In FIGS. 5, 6, and 9 to 13 inclusive, the forms for thepockets and the openings are shown as being applied to both a lift slaband in-situ construction.

Referring to FIGS. 5 and 6, a form for one of the pockets 31 is showntherein with a portion of the form for 7 one of the openings 25 shownadjacent thereto. Said forms comprise wall panel members 38 and cornermembers 39, which are substantially corner posts extending from the topto the bottom of the form on all of the four corners thereof. Referringto FIG. l1. it will be noted that the wall panels 38 have beveled endedges 4) that seat against oppositely beveled vertical walls 41 on thecorners posts 39. Said corner posts have an arcuate body portion 42terminating in the thickened end portions 43 that are provided with thebeveled vertical edges 41. Said corner posts 39 have inwardly extendingbracket portions 44 at the top and bottom thereof, the bracket 44 at thebottom of each post 39 being reversed in position from the bracketportion 44 at the top thereof. Said bracket portions are spaced from theopposite extremities 45 of said post-like members 39. Said post-likemembers are reversible, that is, the same can be reversed top for bottomand all the post-like members are interchangeable. Adjacent each bracketportion 44 is a horizontal shoulder 46, which provides a flat face onthe post 39 and a straight wall portion 47 is provided on the inner faceof the curved wall portion 42 at the shoulder 46. The bracket isprovided with a socket portion 43 and has a portion 49 projectinginwardly beyond the shoulder 46 that has a fiat wall 56 thereon. Saidbracket 44 also has a pair of laterally extending portions or arms 51thereon, each of which has a substantially vertically extending portion52 terminating in a at terminal edge 53 and a cylindrically curvedportion 54 forming a socket in each of said portions 51. The portions 51of said bracket are connected by means of a connecting portion 55, whichhas a at edge that is a continuation of the edge 53.

Cooperating with the bracket 44 is a clamping plate 56, which has a flatbody portion, the under face of which is adapted to engage the shoulder46, and wing portions 57 that are of a semi-cylindrical character havinga curved wall portion 53 and a at wall portion 59 connecting theopposite ends of the curved portion S. The clamping plate 56 ispreferably provided with an obliquely extending edge portion 6i) that islocated adjacent the straight or flat portion 47 of the curved wall 42.The clamping plate 56 is provided with an opening 61 therein, throughwhich the shank of a headed member 62 extends, said headed member havinga head 63 located adjacent the ilat outer face of the clamping plate 56.A nut 64 is engaged with the opposite end of the member 62, being fixedthereto by welding or otherwise so that the nut 64 will servesubstantially as a tixed head on the headed member 62 at the oppositeend thereof from the head 63. The member 62 also extends through anopening 65 in the bracket 44 axially aligning with the socket 48, and acompression 'coil spring 66 is mounted in the socket between theclamping plate 56 and the bottom wall of said socket 48. Thescrew-threaded shank of the member 62 engages with the screv -thrcadsprovided in the opening 65 so that the rotation of the headed member 62by engagement of a tool with a head 63 thereof will move the headedmember bodily up and down relative to the bracket 44 and thus theclamping plate 56 up and down with respect to the bracket 44.

Extending between each of the corner posts 39 along the inner faces ofthe wall panels 38 are holding means comprising bars 67, which are shownas being in the form of hollow tubular members, such as ordinary pipes.The ends of the pipes 67 may be either smooth or threaded and,preferably, are threaded to aid in the gripping action of the clampingmeans, as will be described below. The threads 68 on the ends of thepipes 67 preferably engage corresponding serrations 69 in the curvedwall portions 54 of the socket forming portions 51 of the brackets 44.It will be obvious that upon rotation of the head 63 of each of theheaded members 62 the clamping members 56 on each of the post-likemembers will clamp the threaded ends 66 of a pair of pipes 67 in thesockets provided by the curved portions S4 of the portions 51 of saidbrackets 44, the two pipes thus clamped extending at right angles toeach other. It will also be obvious that upon rotation of the head 63 ofone of said headed members 62 in the opposite direction, the action ofthe coil spring 66 will cause the clamping plate 56 to be moved awayfrom the bracket 44 to space the clamping portions 57 from the socketportions 54 and thus release the pipes 67 from the brackets. It willalso be noted that the passages within the brackets for accommodation ofthe pipes extend backwardly from the portions at which the clamping ofthe pipes takes place, so that the pipes 67 can be removed from thecorner posts by first moving one end inwardly toward the outer rimportion of the corner post with which it is assembled sufficiently towithdraw the oposite end thereof from the socket of the corner postopposite that into which it has been moved further inwardly, whereuponthe corner post so released can bc removed and the pipe then removedfrom the other corner port with which it has remained assembled bywithdrawing the same therefrom, as the opposite corner post will nolonger be interfering with the disengagement of the pipe therefrom. Withthe assembly of the corner posts and pipes the opposite action will, ofcourse, take place.

If the heads 63 of the headed members 62 are not readily accessible inthe lower ends of the posts because of being on the under side of theform, the adjustment of the clamping means can be made by engaging thehead formed by the nut 64 with a suitable tool, the head portion 64being in an accessible position at the upper side of the bracket portion44 on the lower end of the post 39. It will be noted that theenlargements 43 have sockets 70 therein, which are provided for thepurpose of inserting the ends of U-shaped tie members 71 into the samewhereby the forms are spaced from each other the proper distance to getthe desired thickness of the wall between them, such as the framemembers 22, for example. The proportion of the parts is such that theedges 53 of the portions 51 and the edge of the connecting portion 55are in transverse alignment with the top edge of the pipes 67, as willbe obvious from FIG. 12. The top wall panel 72 of the form rests on thepipes 67 at the top of the form and on the edges of the portions 51 and55 aligning therewith. The bottom wall panel 73 is mounted in positionbelow the pipes 67 at the bottom of the form and is suspended therefromby suitable brackets 74, which are detachably mounted on the wall panel73, any desired or necessary number thereof being provided forsupporting the bottom wall panel 73.

In FIG. 6 a completely assembled form is shown for forming oneof .thepockets or chambers 31 at the margin of the solid concrete portion 21,and has a bottom wall 73 spaced a predetermined distance from asupporting surface 75 .by suitable means, such as chairs 76. A box-likeenclosure is thus provided spaced from the supporting surface 75, whichmay be a floor slab of concrete or similar material, in the case of alift slab, a bottom wall of a suitably supported form being substitutedfor the slab 75 in `the case of in-situ pouring of the concrete. It willbe noted that the top edges of the side walls 38 are located above thetop surface 77 of the concrete 21 poured around said form and, ifdesired, beveled strips 78 may be provided along the walls 38 below thetop edges thereof, as shown in FIG. 6, or adjacent said top edges asshown in FIGS. 9 and l() to provide recesses in the poured slab aroundthe pockets and openings created by the forms to permit the setting of aremovable slab on the shoulders resulting around the top of said pocketsor openings. The portions of the forms for the openings 25 shown inFIGS. 5 and 6 are of the same construction as the form for the pocket,except that there is no necessity of providing a .bottom wall 73 in saidforms. The corner posts 39 and the wall panels 3S, as well as the topwall panel 72, are constructed and mounted in the same way for theopenings 25 as for the pockets 31. The forms for the openings 25 would,as shown in FIG. l, have longer wall panels 38 than the pockets 31,while the Wall panels 38 for the pockets 32 would include wall panels ofthe same length as for the openings 25 and shorter wall panels for theshorter walls of the pockets, since these are shown as beingconsiderably longer than they are wide.

In constructing the grid structure for lift slab construction, thebottom edges of the Wall panels 38 are seated directly on the oor slab75 on which the lift slab is to be poured. The adjoining forms arepositioned in the proper spaced relation by means of the tie members 71and triangular cant strips 79 may be provided at the lower edge portionsof the walls 38 on the outer sides thereof, as shown in FIG. 9. If theslab is cast in-situ, the bottom edges of the walls 38 of the forms aremounted on suitable bottom form members 80 for the joists 22 that aremounted on suitable shores 81, and which are provided with side walls 82to form a channel member receiving a pair of walls 3S therebetween.

Should it be desired to vary the rectangular shape of the pockets from asquare or oblong rectangle to another quadrangular form, such as atrapezoidal pocket, such as the pockets 25', then the same corner posts39 are used as in .the other pockets, but a pair of the wall panels 38that provide the obliquely extending walls of the pockets are sawedsomewhat differently at the ends thereof that engage with the cornerposts 39 so that these wall panels 38 willrinterit with the obliquelyextending edges 41 of the corner posts 39 in a similar manner to thatshown in FIG. 11 for the wall panels 38, and instead of providingstraight pipes 67, the pipes 67 are provided on two sides of the form,which are bent at their ends to provide socket receiving portions thatextend parallel to each other at opposite ends thereof, with the mainbody portions thereof extending obliquely to said end portions so thatsaid pipes 67 will engage firmly against the corresponding wall panels38. In FIG. 7 the pocket 33 is shown as being formed by means of sidewall portions 83 and an end wall 84 spaced from the outer wall 85 of theform. The top wall 72 of the form for the pocket 25 has to be shaped tocorrespond to the angular relationship of the side walls 38 `to the sidewalls 38, as is obvious. In the case of both the top walls 72 and 72',the corners are beveled, as at 86, to provide for a proper iit betweenthe top wall and the corner posts. The bottom wall of the form, whensuch is used as shown in FIG. 6, is similarly beveled at the corners. v

Referring to FIGS. 2 and 3, the lift slab that has been poured on asuitable support, such as Va concrete slab 75, is shown as having beenraised into position. In pouring the slab, openings are left in thesolid portion 21 thereof for the posts, the openings being sufficientlylarge that the main body portions 87 of said posts will lit loosely inthe openings provided in the slab. A suitable form is used for formingthe opening in the slab so that a plurality of obliquely extending faces8S and 89 alternate'alongrthe sides of said opening, forming ribs 90 ofa saw-tooth character projecting into the opening. The opening is ofsuch -a size ythat even with the form left in place, which may be asheet metal formY for the sake of thinness, the main body portion 87 ofthe post will slide through the opening as the slabis lifted to theposition it is to have in use. The upper end portion 91 of the post isreduced in diameter to provide a shoulder 92 surrounding the samebetween the main body portion S7 and the reduced portion 91. In formingthe reduced portion, apcorrugated tubular member is preferably utilizedas a form for said upper end portion of the post so that a series ofcorrugations 93 run around said post in the reduced upper end portionsthereof projecting toward the ribs 90 in the opening in the slab. Ifdesired, a spiral reinforcement 94 may be provided in the post,extending into the reduced upper end portion 91 as shown.

After the slab has been poured and has set to its proper structuralstrength the tension members 27, 28, 29 and 30 are tensioned and aftersuch tensioning has been done the slab is raised to the position shownin FIG. 2. While the means for raising the slab is retained in positionto hold the slab in its final position, a quick setting early highstrength concrete filling 95 is poured into the space between the wallsof the opening in the solid concrete slabportion 21 and the reducedportion 91 of the post to completely ll the space between the shoulder92 and the top edge of the opening and between the ribs 90 and thecorrugations 93. After this filling has set to substantially fullstrength, the holding means are removed. The slab is thus mounted on theposts without the use of any shear collars or any other metal structurethat has been previously found necessary. The posts and the slab will befirmly keyed together so that the slab will be firmly mounted on theshoulder 92 on the post 20. Portions of the means previously used forlifting the slab that are in engagement with the concrete are shown inposition in FIG. 2 and comprise headed rod-like rnembers 96 that areprovided with suitable threaded ends 97 for engagement with a pullingmember and a bearing plate 9S that is adapted to receive the thrust ofthe pulling apparatus against the top end of the column 20. While FIG. 2illustrates the top or yupper end of a column, it is obvious that such ashouldered arrangement can be provided at any point along a column wherea lift slab is desired to be mounted on a shoulder such as the shoulder92 provided on the column 20. The headed members 96 are removable fromthe concrete, being wrapped with paper or other suitable material toprevent bonding of these in the concrete 21 and thus all of the liftingapparat-us is disengageable from the slab for use in another location assoon as the lifting operation has .been completed.

After the forms have been removed any desired type of decking may beprovided on the grid structure and any desired cover slab may beprovided over the pockets provided in the margins of the solid concretestructure 21 around a column. In FIG. 8 a removable slab 99, which isshown as being of concrete but which may be of any other desiredmaterial, is shown as being mounted on the dividing wall 100 between anopening 25 and the pocket 31, the pocket having a bottom wall 101, whilethe opening 25 is open at the bottom. The covering slab 99A is shown asextending across the dividing wall 100 which aligns wit-h one of theframe members 22 and thus for-ms a portion thereof, and as Ibeing seatedin a groove or recess 102 in the concrete body 21, which has been formedby means of the wedge-like strip 78 that was mounted on the one wallmember 38 of the form for the opening 31 shown in FIG. 6.

In FIG. 14 is shown a pair of frame members 22 intersect-ed by a framemember 23 to provide a grid structure having the openings 25 therein andcover slabs 99, 103

and 104 are shown as being mounted over said openings 25 with the end ofthe cover slab 99, which may be assumed to be a continuation of the slab99 shown in FIG. 8, in abutting engagement with the slab 103 over theframe member 22 and with the slabs 103 and 104 in butting engagementwith each other over the frame member 22.

Instead of providing such an arrangement as shown in FIG. 14 for thecover slabs, the cover slabs 105, 106 and 107 are shown in FIG. 15 asbeing mounted on frame members 22, which are the same as the framemembers 22 except for the fact that grooves 108 have been providedtherein in a similar manner to that disclosed for the pocket 31 in FIG.6. The beveled ends of the cover slabs 105, 106 and 107 are seated insaid grooves or recesses 108 with the top surface thereof flush with thetop surfaces of the frame members 22". Obviously all the marginal edgesof the various cover slabs for the openings in the grid structure inthis mounting of the cover slabs will be similarly beveled and all theframe members on which the same would be seated would have similargrooves or recesses 103 therein for receiving the 1 1 beveled edges ofthe cover slabs. Also, referring to FIG. 8, the top surface of the solidbody of concrete 21 would, in such case, be made flush with the topsurfaces of the frame members 22".

Instead of providing a form for the pockets or openings that is providedwith at wooden wall panels, a metallic form that can be removed upwardlythrough the opening left in the concrete by the form is shown in FIGS.16 to 21, inclusive, and FIG. 24. Said form comprises the metal wallsections 109 that have the vertically extending wall portions 110connected by means of curved wall portions 111, said verticallyextending wall portions 110 extending at right angles to each other.Mounted between the adjacent ends of each of the wall sections 109 arewall portions 112 that complete the quadrangular enclosure of the form.Each said angular wall sections 109 is provided with a box-likereinforcement 113 extending up and down along each of the vertical endedges thereof and the members 112 overlap the box-like reinforcements113 as shown in FIG. 16, said box-like reinforcements projectingslightly beyond the vertical end edges of the wall sections 109. Each ofsaid members 112 is provided with a stitfening means extendingvertically of the same, comprising the obliquely extending walls 114connected by means of a transverse wall portion 115.

Each of the wall portions 116 of the wall sections 109 is provided witha box-like reinforcement 116 along the upper margin thereof, and asimilar box-like reinforcement 117 along the lower margin thereof. Thetop and bottom reinforcements are connected at the curved cornerportions 111 of the wall sections by means of plate-like members 118that are welded to the box-like reinforcements 116 and 117, saidbox-like reinforcements being welded to the vertical wall members 11) inany suitable manner. The portions 115 of the stiifening members for theintermediate wall forming members 112 are provided with a plurality ofkeyhole slots in each end thereof, the endmost keyhole slot beingindicated by the numeral 119, the intermediate slot of each row by thenumeral 120 and the innermost slot by the numeral 121. The inner walls122 of the stiifening formations 113 are each provided with a similarkeyhole slot 123.

Each of the forms is provided with a pair of transversely extendingbraces 124 and 125. The braces 124 and 125 are the same in construction,but are located somewhat differently in the form, as will be explainedbelow. Each of said transverse braces is provided with a main bodyportion 126 and an adjustable portion 127 telescopically received withinthe main body portion 126. The connection between the portions 126 and127 is shown more in detail in FIG. 21, the member 127 beinglongitudinally slidably mounted in the member 126 and each of themembers being provided with slots for reception of a locking wedge 128.The inner member 127 is provided with a plurality of opposite pairs ofslots 139, which are arranged at regular distances along said member 127so that a wedge 128 may be passed through the single pair ofdiametrically opposed slots 130 in the lof said members 124 and 125 isprovided with a plug 131 xed in each end thereof, as by means ofwelding, one of said plugs being mounted in the end of the main bodyportion 126 of each of said braces on the opposite end thereof from thathaving the slots 130 therein and the other plug 131 being mounted in theunslotted end of the member 127 of said transverse brace. The adjustmentof the members 126 and 127 is made such that Athe plugs 131 willproperly cooperate with the keyhole slots in the stitfening formationson the members 112. In order for the plugs to cooperate with saidkeyhole slots, each of said plugs is provided with a head portion 132and a reduced neck portion 133 that spaces the head portion 132 from themain body portion of the plug 131. The neck portion 133 is of a diametersuch that it will t snugly in the smaller portion 134 of the keyholeslot with which it is associated, while the head portion 132 of each ofsaid plugs is of such a size as to readily pass through the enlargedportion 135 of each of said slots. The keyhole slots, it will be notedupon reference to FIG. 17, are reversed so that the lower transversebraces 124 and 125 will be interlocked with the stiffening formations onthe members 112 by an upward movement thereof, while the upper bracingmembers 124 and 125 will be interlocked therewith by a downward movementthereof.

The bracing members 124 have the headed plugs 131 thereof mounted in theuppermost and lowermost keyhole slots 119, while the heads on the plugmembers 131 of the transverse braces 125 engage in the keyhole slots120, thus locating the main body portion of the transverse bracingmember 125 at the top and bottom of the form closely adjacent thetransverse bracing member 124 at said top and bottom. The transversebracing members 124 provided at the top and bottom of the form,respectively, have the outermost portions thereof in transversealignment with the top surfaces 136 and the bottom surfaces 137 of thetop bracing formations 116 and bottom bracing formations 117 of saidwall sections, respectively. The upper brace 124 and the stilfeningformations 116 thus serve as supporting means for a top wall panel 138,while the stiffening formations 117 and the bottom transverse brace 124serve as supporting means for the bottom wall panel 139, Z-shapedbrackets being provided on the bottom wall panel members 139 formounting the bottom wall panels on the form, said brackets 140 beingdetachably secured by suitable securing elements 141 to the bottom wallpanel 139.

Transverse bracing means 142 is provided adjacent the top and bottom ofeach of the vertical walls of the form at the connection between theangular wall forming sections 109 and the intermediate wall formingmembers 112, said bracing members 142 being of a U-shaped cross sectionand having a plurality of headed members 143 extending through the webportion 144 thereof. Each of said headed members 143 has a head 145 onthe inner side of the web portion 144 and a head 146 spaced from thehead 145 by a narrow neck portion 147. The heads 146 are of such a sizethat they will readily pass through the enlarged portions 135 of thekeyhole slots 121 and through similar enlarged portions of the keyholeslots 123 provided in the vertical stiffening formations 113 in the wallforming sections 109, while the narrow neck portions 147 will fit snuglyin the smaller portions of said keyhole slots 123 and 121. It willaccordingly be obvious that by inserting the reinforcing member 142 withthe heads 146 on the headed members 143 thereof in the enlarged portionsof the keyhole slots 121 and 123 and then moving the reinforcing bar 142downwardly, in the case of the upper reinforcing bar, or upwardly, inthe case of the lower reinforcing bar, the reinforcing bars 142 will beinterlocked with the wall forming members 112 and 109 in such a manneras to transversely brace the same.

It will be noted upon reference to FIG. 17 that with the transversebracing members 124 and 125 in position and with the wedges 128 insertedtherein to hold the members 124 and 125 in proper adjusted position, theoverlapping edge portions 148 of the member 112 will be in engagementwith the outer faces of the stiifening formations 113, while thetransverse bracing members 142 will be in engagement with the innerfaces of said stiifening formations 113, and that the transverse braces124 and 125 will hold the members 112 from movement toward and away fromeach other and thus relative to each other.

v The form will thus be held in its proper quadrangular will also benoted upon reference to FIGS. 18 to 21 inclusive, that the verticalwalls 11@ of the wall sections 109 have portions 149 that extendvupwardly above the top walls 136 of the longitudinal stiffening members116 to thus Vprovide means for coniining the top wall panel 13S withinthe side walls'Y of the form. Similarly, the side walls 110 haveportions 150 that extend beyond the bottom walls 137 of the longitudinalstiifening formations 117 to similarly confine the bottom wall panels139 within the side walls of the form.

Referring to FIG. 22 the form shown therein is shown as having asidewall portion 110' that has a stiifening formation 116 running along thesame and has a recess forming projection 151 detachably mounted thereonby means ofa suitable fastening element, such as the bolt 152, therecess forming formation 151 being shown as of a circular character andas hollow, although the particular structure thereof may be varied asmay be found desirable. Said member 151 for forming the projection onthe form should, however, be of a tapering character such as shown inFIG. 22, to make the withdrawal of the form from the concrete easier.The wall 110 of the form shown in FIG. 22 is the same as the wall 110 ofthe form previously described, the only diiference in the forms beingthat the recess forming member 151 is provided thereon. Said recessforming member is mounted in such `a position that the recess 153provided in the vertical wall 154 of the concrete structure, in whichthe opening or pocket is formed by means of the form, is located thethickness of a top wall panel 138 below the top surface of the wallportion 154 that has been poured around the form. Accordingly, when itis desired to provide a deck slab 155 on top of a gridslike structurehaving the wall portions 154 by pouring the same, a supporting panel 156for the slab that is to be poured can be mounted on the transversebracing member 124, the plug portion 131 of which may be seated in arecess 153 and a corresponding recess similarly cast in a wallcorresponding to the wall 154 transversely across from the recess 153.Obviously a desired number of such recess forming members 151 may beprovided on the forms in the desired locations for providing theopposite pairs of recesses 153 for mounting any desired number orarrangement of, transverse bracing members 124 in position on agrid-like structure for supporting panels similar to the panels 156 tobe utilized under a poured slab such as the slab 155. After the slab hasbeen poured and the concrete has set, the bracing members 124 can beremoved by removing the wedges 128 and telescoping the portions 127thereof within the portions 126 to remove the headed plugs 131 from therecesses 153, whereupon the Ypanels 156 can be removed downwardlythrough` the openings 25 in the grid structure.

What I claim is:

1. Inconcreteconstruction a lift slab having rectangular openingstherein, Ya solid area of uniform thickness surrounding each of saidopenings, supporting columns for said slab, means in each of said solidareas of said slab for prestressing, said, area to compress said areatoward the center of said opening, comprising a plurality ofprestressing members extending across said area on each side of saidopening and comprising prestressing members extending perpendicularly toone pair of opposed sides of said.opening and prestressing membersextending perpendicularly tothe other pair of opposed sides of saidopening, and means for supporting said slab on said column comprising awide, ilat upwardly facing shoulder on eachrof said columns spaced fromthe upper end thereof and lreduced portions circular in cross section onsaid columns extending upwardly from said shoulders andmounted in saidopening, horizontal ribs on the walls of said openings projecting towardsaid reduced portions and high strength concrete filling said openingsand extending into engagement with said shoulders and between said ribs.

2. In a building construction, columns having reduced end portionsproviding shoulders thereon, and a reinforced monolithic concretestructure mounted on said columns comprising an area of solidprestressed concrete of uniform thickness adjacent each column extendinghorizontally beyond said column in all directions, and each centrallysupported on a column, said area having an opening receiving saidreduced end portion of said column and a grid-like structure integrallyunited with and extending between said solid concrete areas, saidgrid-like structure comprising spaced longitudinally extending andspaced transversely extending prestressed frame members, saidlongitudinally and transversely extending frame members intersecting andbeing integrally united to dcne openings extending through saidstructure between the same, certain of said longitudinally extending andcertain of said transversely extending frame members intersecting saidsolid areas, means for compressing each of said solid areas toward thecenter of said column receiving opening, comprising prestressing membersextending longitudinally within both the longitudinally and transverselyextending frame members that intersect said solid area, saidprestressing members being embedded in and extending across said solidarea on opposite sides of said column receiving opening in alignmentwith the frame members in which the same extend, and a plurality ofother prestressing members embedded in and traversing said solid area oneach side of said column receiving opening out of alignment with theframe members, said other prestressing members including prestressingmembers extending in parallelism to each of the prestressing membersaligning with said frame members, and a concrete filling in said columnreceiving openings between the walls 'thereof and the reduced endportions of said columns.

3. In a building construction, columns having reduced end portionsproviding shoulders thereon, and a reinf forced monolithic concretestructure mounted on said columns comprising an area of solidprestressed concrete of uniform thickness adjacent each column extendinghorizontally beyond said column in all directions, and each centrallysupported on a column,` and a grid-like structure integrally united withand extending between said solid concrete areas, .said grid-likestructure comprising spaced longitudinally extending and spacedtransversely extending prestressed frame members, said longitudinallyand transversely extending frame members intersecting and beingintegrally united to deiine openings extending through said structurebetween the same, certain of said longitudinally extending and certainof said transversely 4extending frame members intersecting said solidareas, each of said solid areas having a central opening thereinreceiving the reduced end portion of one of said columns, means forcompressing each of said solid areas toward the center thereofcomprising prestressing members extending longitudinally within both thelongitudinally and transversely extending frame members that intersectsaid solid area, said prestressing members being embedded in andextending across said solid area in alignment with the frame members inwhich the same extend and on opposite sides of said central opening andincluding prestressing members extending across said solid area adjacentsaid central 4opening and prestressing members transversely spacedtherefrom and extending across said solid area remote from said centralopening, and a plurality of other prestressing members out of alignmentwith said frame members embedded in said solid area, said otherprestressing members including prestressing members extending parallelto and positioned between said prestressing members that are adjacentsaid central opening and prestressing members that are parallel to andpositioned between the prestressing members that are remote from saidcentral opening and the prestressing members that are adjacent saidcentral opening, and a concrete filling in said column receivingopenings between the walls thereof and the reduced end portions of saidcolumns.

4. In a building construction, columns having reduced end portionsproviding shoulders thereon, and a reinforced monolithic concretestructure mounted on said columns comprising an area of solid concreteof uniform thickness adjacent each column extending horizontally beyondsaid column in all directions and supported on said column, and agrid-like concrete structure integrally united with said solid areacomprising a pair of transversely spaced frame members extending awayfrom said said column on each side of said solid area, the frame membersextending from opposite sides of said solid area being longitudinallyaligned, said structure having open topped pockets between the marginsof said solid area and right angularly intersecting members of saidgrid-like structure, said pockets including pairs of opposed pockets outof alignment with said columns and pairs of opposed pockets in alignmentwith said columns, all said pockets having bottom walls and having adepth greater than half the thickness of said solid area, each of saidsolid areas having a central opening therein receiving said reduced endportion of one of said columns, means for compressing each of said solidareas toward the center thereof, comprising prestressing membersextending longitudinally within said frame members and embedded in andextending across said solid area adjacent said central opening,prestressing members embedded in and traversing said solid area inparallelism to and between the prestressing members, that are adjacentsaid central opening and terminating in the pockets that are alignedwith said column, and prestressing members embedded in and extendingacross said solid area in parallelism to the prestressing members thatare adjacent said central opening, said last mentioned prestressingmembers extending between said pockets that are out of alignment withsaid column and terminating therein, and a concrete filling in saidcolumn receiving openings between the walls thereof and the reduced endportions of said columns.

5. In a building construction, columns having reduced end portionsproviding shoulders thereon, and a reinforced monolithic concretestructure mounted on said columns comprising an area of solidprestressed concrete of uniform thickness adjacent each column extendinghorizontally beyond said column in all directions, and each centrallysupported on a column, and a grid-like structure integrally united withand extending between said solid concrete areas, said grid-likestructure comprising spaced longitudinally extending and spacedtransversely extending prestressed frame members, said longitudinallyand transversely extending frame members intersecting and beingintegrally united to define openings extending through said structurebetween the same, certain of said longitudinally extending and certainof said transversely extending frame members intersecting said solidareas, each of said solid areas having a central opening thereinreceiving said reduced end portion of one of said columns, means forcompressing each of Said solid areas toward the center thereofcomprising prestressing members extending longitudinally within both thelongitudinally and transversely extending frame members that intersectsaid area, said prestressing members being embedded in and extendingacross said solid area in alignment with said frame members in which thesame extend and on opposite sides of said central opening and otherprestressing members embedded in and traversing said solid area inparallelism with each of said prestressing members that align with saidframe members, said other prestressing members extending on oppositesides of said central opening and being out of alignment with said framemembers, each of said columns having a wide, flat upwardly facingshoulder thereon spaced from the upper end thereof, and a high strengthconcrete tilling between the walls of said 15 central opening and saidreduced upper end portion seated on said shoulder and providing meansfor connecting said columns and said solid concrete areas to supportsaid structure on said columns.

6. In a building construction, columns, and a reinforced monolithicconcrete structure mounted on said columns comprising an area of solidconcrete adjacent each column extending horizontally beyond said columnin all directions and supported on said column, and a gridlike concretestructure integrally united with said solid area comprising a pair oftransversely spaced frame members extending away from said column oneach side of said solid area, the frame members extending from oppositesides of said solid area being longitudinally aligned, said structurehaving open topped pockets at the margins of said solid area, saidpockets having a depth greater than half the thickness of said solidarea and including pairs of opposed pockets out of alignment with saidcolumn and pairs of pockets in alignment with said column, said pocketsin alignment with said column each extending between a pair of saidframe members, means for compressing each of said solid areas toward theCenter thereof, comprising prestressing members extending longitudinallywithin said frame members and embedded in and extending across saidsolid area adjacent the center thereof in alignment with the framemembers within which the same extend, prestressing members embedded inand traversing said solid area in parallelism to and between saidprestressing members that align with said frame members, said lastmentioned prestressing members terminating in the pockets that arealigned with said column, and prestressing members embedded in andextending across said solid area between and terminating in said pocketsthat are out of alignment with said column and extending in parallelismto the prestressing members that align with said frame members, saidsolid areas having central openings therethrough in alignment with saidcolumns, each of said columns having a reduced upper end portionproviding a wide, flat upwardly facing shoulder thereon spaced from theupper end thereof, said reduced upper end portion of said column beingmounted in said central opening and a high strength concrete fillingbetween the walls of said central opening and said reduced upper endportion seated on said shoulder and providing means for connecting saidcolumns and said solid concrete areas to support said structure on saidcolumns.

References Cited in the file of this patent UNITED STATES PATENTS999,286 Wilson Aug. 1, 1911 1,678,504 Glover July 24, 1928 2,075,591Schuster Mar. 30, 1937 2,230,153 Allbright Jan. 28, 1941 2,315,634McCall Apr. 6, 1943 2,414,738 Henderson Jan. 21, 1947 2,477,256 KneasJuly 26, 1949 2,531,576 McClellan et al. Nov. 28, 1950 2,715,013 SlickAug. 9, 1955 2,720,017 Youtz Oct. 11, 1955 2,721,369 Burke Oct. 25, 19552,775,019 Bemis Dec. 25, 1956 2,783,638 Henderson Mar. 5, 1957 2,852,931Bonet Sept. 23, 1958 2,929,235 Cheskin Mar. 22, 1960 FOREIGN PATENTS145,214 Sweden 1954 301,716 Sweden 1954 556,570 Great Britain 1943589,804 Great Britain 1947

1. IN CONCRETE CONSTRUCTION A LIFT SLAB HAVING RECTANGULAR OPENINGSTHEREIN, A SOLID AREA OF UNIFORM THICKNESS SURROUNDING EACH OF SAIDOPENINGS, SUPPORTING COLUMNS FOR SAID SLAB, MEANS IN EACH OF SAID SOLIDAREAS OF SAID SLAB FOR PRESTRESSING SAID AREA TO COMPRESS SAID AREATOWARD THE CENTER OF SAID OPENING, COMPRISING A PLURALITY OFPRESTRESSING MEMBERS EXTENDING ACROSS SAID AREA ON EACH SIDE OF SAIDOPENING AND COMPRISING PRESTRESSING MEMBERS EXTENDING PERPENDICULARLY TOONE PAIR OF OPPOSED SIDES OF SAID OPENING AND PRESTRESSING MEMBERSEXTENDING PERPENDICULARLY TO THE OTHER PAIR OF OPPOSED SIDES OF SAIDOPENING, AND MEANS FOR SUPPORTING SAID SLAB ON SAID COLUMN COMPRISING AWIDE, FLAT UPWARDLY FACING SHOULDER ON EACH OF SAID COLUMNS SPACED FROMTHE UPPER END THEREOF AND REDUCED PORTIONS CIRCULAR IN CROSS SECTION ONSAID COLUMNS EXTENDING UPWARDLY FROM SAID SHOULDERS AND MOUNTED IN SAIDOPENING, HORIZONTAL RIBS ON THE WALLS OF SAID OPENINGS PROJECTING TOWARDSAID REDUCED PORTIONS AND HIGH STRENGTH CONCRETE FILLING SAID OPENINGSAND EXTENDING INTO ENGAGEMENT WITH SAID SHOULDERS AND BETWEEN SAID RIBS.